This invention concerns enhanced color removal from colored waste paper, for example, post-consumer colored paper being recycled or colored broke being recycled from a papermaking machine. The method of the invention describes a process for brightening fiber from colored waste paper while increasing fiber web or paper web strength.
In current methods of processing colored waste paper for use in recycled paper products the waste paper is usually bleached prior to forming the new product so that the desired color and brightness can be obtained in the new product. There are a number of problems associated with the recycling of such colored waste paper. These include (1) the presence of residual color from dyes used to dye the paper and dyes used in certain types of printing, and (2) loss of strength of the fiber during processing. Typically, attempts at increasing the brightness have included the use of multiple-stage bleaching with hydrogen peroxide or chlorine-containing oxidative bleaches which adversely affect the pulp strength. In addition, the chlorine containing bleaches may contribute to the formation of chlorinated organics which are environmentally undesirable. Methods to recover the loss of strength have included adding expensive kraft fiber or bonding agents to the pulped material.
There have been a number of attempts at forming improved pulps.
U.S. Pat. No. 4,710,267 to Elsby et al discloses dye removal from recycled fiber using tertiary or quaternary ammonium compounds. These ammonium compounds have a carbonyloxy portion. Customary bleaching agents may be used in conjunction with these ammonium compounds.
Japanese patent application Number 82/25489 teaches color removal by washing the pulp with alkylamine-propoxylates-ethoxylates.
U.S. Pat. No. 2,003,928 to Evans et al describes enhanced bleaching of textiles containing azoic dyes with the use of sodium dithionite and a quaternary ammonium salt having not less than 10 carbons.
U.S. Pat. No. 5,013,404 to Christiansen et al describes the alkaline hydrogen peroxide bleaching of mechanical wood pulp with a quaternary amine compound with an hydroxy group such as (3-chloro-2-hydroxypropyltrimethyl)ammonium chloride.
U.S. Pat. No. 3,554,863 to Hervey et al teaches the use of cationic quaternary amine compounds as debonding agents for pulp sheets. The use of such compounds lowers the tensile strength of the sheets.
U.S. Pat. No. 3,617,439 to Chapman describes a method for improving comminution of pulp sheets from cellulosic fibers in order to make fibers from which air-laid absorbent products may be prepared. The method includes the use of a quaternary zwitterionic surfactant.
U.S. Pat. No. 4,144,122 to Emanuelsson et al describes the use of quaternary ammonium compounds to treat cellulose pulp and paper to reduce inter-fiber bonding and thereby obtain a low mechanical strength for the fibers.
U. S. Pat. No. 4,441,962 to Osborn discloses a process for making absorbent tissue paper webs using quaternary ammonium compounds as debonding agents to weaken the strength of the interfiber bonds.
U.S. Pat. No. 4,632,730 to Ulubay et al discloses a method for increasing the absorption rate of paper using selected ethoxylated and/or propoxylated compounds.
U.S. Pat. No. 5,129,987 to Joachimides et al discloses a method of bleaching mechanical wood pulp with sodium hydrosulfite in a refiner.
Enhanced bleaching of textiles containing dyes is described in Dyeing and Chemical Technology of Textile Fibers, by E. R. Troutman (fifth edition, Charles Griffin and Co., Ltd., 1975).
There still remains a need for a method of decolorizing colored waste paper which will result in a well bleached pulp and particularly one with significant increase in fiber strength. Thus, it is an object of the present invention to provide such a method. It is a further object of the present invention to provide a method for recycling colored waste paper which results in a pulp which can be used to form acceptable recycled products. It is yet another object of the invention to provide a process for recycling colored waste paper which is acceptable environmentally. These and other objects of the invention will become apparent from the description of the invention.